Dental impression trays are used by dentists, orthodontists, prosthodontists and others in the field of dentistry to make models of a patient's teeth or other specific areas of a patient's oral cavity. Dentists and prosthodontists make impressions for the purpose of making false or replacement teeth, or for the preparation of restorative crowns, bridges and the like. Orthodontists make impressions to study malformations of the teeth and jaws and plan a course of treatment. Orthodontists also use impressions to size and manufacture dental appliances.
To obtain a dental model, an impression of desired areas of the patient's mouth is first obtained. To prepare an impression, a quantity of curable dental impression material is placed in an impression tray, and the tray is then positioned in the patient's mouth. The impression material fills and surrounds the selected area of interest of the mouth. Once the impression material has cured, the impression material along with the tray is removed from the mouth. A second curable material is then poured or otherwise placed in the cured impression material. Once the second material has cured, the impression material is removed from the resulting model, which provides an accurate physical replica of the patient's tooth structure and adjacent portions of the patient's gingiva.
A common problem with prior art dental impression trays is that they usually induce a gag reflex when placed in a patient's mouth. This is best appreciated by first understanding the nature of the pharyngeal reflex (gag).
The pharyngeal reflex (gag) is caused by the contraction of the constrictor muscle of the pharynx, elicited by touching the back of the pharynx. In normal swallowing, in the first stage of deglutition, the bolus of food is driven back into the fauces by the pressure of the tongue against the hard palate. At the same time, the base of the tongue is retracted and the larynx raised with the pharynx. During the second stage, the entrance to the larynx is closed by the drawing forward of the arytenoid cartilages toward the cushion of the epiglottis, a movement produced by the contraction of the thyreoarytaenoidei, the arytaenoidi and the arytanoepiglottidei (muscles of the back of the throat). As soon as the bolus of food is received in the pharynx, the elevator muscles relax, the pharynx descends and the constrictors contract upon the bolus and convey it downward into the esophagus.
When a properly designed dental impression tray is placed in the mouth, the second stage of the swallowing response is stimulated as described above by the application of pressure in front of the highly innervated delineation between the hard and soft palate. An improperly designed tray, then, does not apply pressure in front of the delineated space between the hard and soft palate.
A variety of dental impression trays are known in the art. However, none of them are suitable for taking an impression of a patient's maxillary dentition while simultaneously preventing a normal physiological "gag" response to placement of the tray in a patient's mouth. Quite simply, conventional prior art dental impression trays are not designed to prevent a normal gag response which occurs when the tray is placed in a patient's mouth.
One example of a patented dental impression tray is disclosed in U.S. Pat. No. 3,737,663 (White). This patent discloses a set of trays for taking impression of both the maxillary (upper) and mandibular (lower) dentition. Although this patent suggests that one of the patented trays (maxillary) is designed to prevent gagging during use (see, col. 5, lines 10-19), the patented tray is designed to only take an impression of the maxillary dentition, and not the palate.
Another patented maxillary dental impression tray is disclosed in German Patent No. 885,595 (Gruber). Gruber's tray includes an elevated floor portion (see, FIGS. 1-2) and is therefore capable of taking an impression of the patient's palate. However, the arched plan floor of the tray surrounding the elevated portion is open-ended in the back of the tray, which causes the aginate impression material to leak out the back of the tray. Moreover, the elevated portion of the floor has a greater height than the peripheral wall (see, FIG. 2) which causes the tray elevated floor portion to contact the palate during use, and also causes aginate to flow over the peripheral wall, as shown in FIG. 2 of the patent. If the elevated portion of the floor contacts the soft palate, gagging will occur. It does not appear from the patent drawings that the elevated floor section is indented from the posterior wall of the tray to ensure contact only with the hard palate.
What is needed then, is a dental impression tray for the palate and maxillary dentition that will prevent gagging during use.